14G MacDougal, The Physiology of Tendrils. 



irritability of tendrils published three years ago (2) his astonishmeut 

 would not have been so great, since I distinctly announced that. 

 I found such a relation of tendrils to temperature in the following 

 words: „Drops of water at ordinay temperatures thrown either 

 gently or forcibly against the tendrils produced no curvature". 

 If the temperature of the water in the previous experiment were 

 raised to 40° C curves were produced: or if a sraall rod heated 

 to 50° C were lield near the tendril like results followed." In 

 experiments with ice I used only sraall pieces which when rubbed 

 against the tendril were covered with a layer of water, and were 

 inoperative on this account as contact Stimuli while their mass was 

 not sufficient to lower temperature to such an extent as to act as 

 Stimuli. These experiments were carried on in November 1892 in 

 a plant house at a temperature of 22 ° C — 26 ° C. 



In the low temperature tests Herr Correns has brought out 

 many new and interesting reactions, but I am not able to agree 

 with him in his conclusions concerning the general nature of tem- 

 perature reactions. The disparity between the sensibility of tendrils 

 to contact and temperature Stimuli, the fact that a gradual increase 

 of temperature acts as a Stimulus, (3) and that Webe r's law may 

 not be applied to the reactions point to the inference that the 

 temperature curvatures are not entirely due to the special irrita- 

 bility of the tendrils but to conditions operative in other organs 

 as well: a conclusion which I reached in my original work. „The 

 results of these high and low temperature Stimuli are doubtless 

 due to their direct influence on the osmotic action of the cells, 

 since in the experiment with the heated rod the tendril can be 

 made to curve backward." 



Herr Correns has also seen fit to disregard my work upon 

 the chemical irritability of tendrils. In killing and fixing material 

 for use in obtaining sections by the paraffin imbedding method, 

 I found that a mixture of alcohol, Chloroform, and acetic acid would 

 kill and fix the protoplasm almost instantly and before any but a 

 very slight curvature had been produced, although each of the 

 three components of the mixture would cause the tendril to assume 

 the form of a helix when used separately. 



As to the mechanism of curvature, I have now in press the 

 results of some extended work which point to the conclusion that 

 curvatures are to the activity of the tissues of the convex, or 

 irritable side of the tendril. 



1. Correns, C, Zur Physiologie der Ranken. (Bot. Ztg. 1 Abth., 

 Heft 1. 16. Jan. 1896.) 



2. Mac Dougal, D. T., Tendrils of Passiflora caerulea. IL Ex- 

 ternal phenomena of irritability and coiling. (Bot. Gazette. Vol. 

 XVIII. p. 123—130. 1893.) 



3. Mac Farlane has found similar relations to obtain in Dionaea 

 muscipula. Contributions to the history of Dionaea muscipula. 

 (Ellis. Cont. Bot. Lab. Univ. of Pennsylvania. Vol. I. No. 1. 

 1892.^ 



